Pigmented coating compositions are useful for their aesthetic as well as protective features. Such compositions often contain a film-forming resin and a pigment dispersed in a liquid carrier. It is important that the pigment be satisfactorily dispersed throughout any film which results from the application of the coating composition. It is therefore desirable that the pigment be well dispersed throughout the liquid coating composition. Typically, the pigment to be used in a coating composition is first dispersed with only a portion of the total film-forming resin of which the coating composition is comprised (often referred to as a pigment “grind resin”) together with appropriate liquid carriers and additives. The resulting dispersion is then mixed with the remainder of the film-forming resin and any other necessary components to produce the coating composition.
A number of different film-forming resins are used in the manufacture of different coating compositions. As a result, so-called “multi-purpose” pigment grinding resins have been used that are compatible with a wide range of film-forming resins and solvents.
Exemplary of such “multi-purpose” pigment grinding resins are the amine functional acrylic grind resins described in U.S. Pat. No. 4,303,764. Due to their relatively low molecular weight, however, these grind resins may be undesirable for use in preparing coatings having the physical properties, such as solvent resistance, necessary for use in many applications. Another example of such “multi-purpose” grinding vehicles are the acrylic polymers having pendant tertiary alkyl primary amine groups and at least one other pendant functionality reactive with isocyanate groups described in U.S. Pat. No. 4,910,249. The cost and lack of commercial availability of the amine-group containing monomer used to make such grind vehicles, however, makes these grind vehicles unattractive commercially for coatings to be used in many applications.
As a result, it is desired to provide “multi-purpose” pigment dispersions that include a pigment grind resin that is prepared from relatively low cost and readily available monomers and which is capable of use in coating compositions designed for use in applications in which the coating must be particularly resistant to exposure to organic solvents.